1. Field of the Invention
This invention relates to a field effect semiconductor device, and more particularly to a field effect semiconductor device in which the gate length per given area of a semiconductor substrate is great to provide a large output and which is adapted to provide an excellent frequency characteristic.
2. Description of the Prior Art
Field effect transistors (hereinafter referred to as FET's for the sake of brevity) are far higher in input impedance than bipolar transistors, and hence they have advantages such as requiring small driving power therefor and exhibiting low noise, even in the case of a signal source impedance being high. However, the typical FET's have an extremely small capability of handling high electric power, as compared with the bipolar transistors. One of the reasons therefor lies in the electrode structure employed in the FET's. Two solutions are considered possible therefor: One is to increase the gate length per one unit such as a source or drain electrode and the other is to increase the degree of integration of units on a given semiconductor substrate and actuate the units in parallel, thereby to obtain a large output as a whole.
These two solutions are contradictory to each other but, eventually, it is necessary to maximize the opposing length between pluralities of source and drain regions formed on a semiconductor substrate, increase the area occupied by each of the source and drain region, and cause a uniform operation over the entire area of the semiconductor substrate. Further, it is also necessary to prevent local overheating due to nonuniformity of current density caused by local nonuniformity in impurity concentration and in diffusion depth in each of the source and drain regions.